The goal of this study is to perform an ex-ante life cycle assessment (LCA) of the emerging gallium-arsenide nanowire tandem solar cells on silicon (GaAs/Si) and to provide a benchmark for the commercialization of the technology. The environmental impacts and energy payback time (EPBT) of the GaAs/Si modules are compared with those of the incumbent single-Si modules. Parameters and efficiencies most relevant to be optimized in order to commercialize the technology are identified and discussed. Two production routes for GaAs/Si solar cells are being up-scaled: the growth of GaAs nanowires on a native substrate, peel-off, and transfer to a silicon substrate (transfer route) and the direct growth of GaAs nanowires on a silicon substrate with assistance of a silicon-dioxide (SiO2) nanotube template (direct growth route). Two ex-ante LCAs for the different manufacturing routes and an LCA for the incumbent single-Si technology were conducted. Environmental impacts of the GaAs/Si technology were assessed and compared with the incumbent. Various scenarios regarding sensitive parameters and processes were modeled—such as modeling several industrial scale tools, the energy consumption of sensitive processes, the number of substrate reuses, the frequency of re-polishing the wafer, and benchmarking the scale of improvement of major impact drivers. The analysis showed that, if expected process efficiencies are achieved, a 28% efficient GaAs/Si module performs 5 to 20% better (transfer route) and 20 to 30% better (direct growth route, except the ozone depletion impact) compared with an 18% efficient single-Si module, for all impact categories assessed—climate change, land use, acidification, ozone depletion, freshwater, marine, terrestrial ecotoxicity, eutrophication, human toxicity, and photochemical oxidation. Critical hotspots identified include the use of gold, trifluoromethane (CHF3), and a GaAs wafer. The EPBT of the GaAs/Si nanowire tandem module is in between 1.37 (expected process efficiencies achieved) and 1.9 years (worst case scenario), while the EPBT of the single-Si module is 1.84 years. Results can be considered as a benchmark for the successful commercialization of the technology. If 28% efficient GaAs/Si nanowire tandem modules are developed, expected process efficiencies are achieved, and at least 100 reuses of the GaAs substrate (transfer route) are realized; then, the GaAs/Si modules perform better compared with an 18% efficient single-Si module for most impact categories assessed. Conclusions from the ex-ante LCA are conditional (if-then) and can be used as a benchmark, allowing to quantify the efficiencies that need to be achieved to commercialize the technology.

中文翻译：

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基于 GaAs/Si 纳米线的串联太阳能电池的事前生命周期评估：工业化的基准

本研究的目标是对新兴的硅上砷化镓纳米线串联太阳能电池 (GaAs/Si) 进行事前生命周期评估 (LCA)，并为该技术的商业化提供基准。将 GaAs/Si 模块的环境影响和能源回收时间 (EPBT) 与现有的单硅模块进行比较。确定并讨论了最相关的参数和效率，以优化该技术的商业化。GaAs/Si 太阳能电池的两条生产路线正在扩大规模：在原生衬底上生长 GaAs 纳米线、剥离并转移到硅衬底（转移路线）和在硅衬底上直接生长 GaAs 纳米线借助二氧化硅 (SiO2) 纳米管模板（直接生长路线）。对不同的制造路线进行了两次事前 LCA，对现有单晶技术进行了一次 LCA。评估了 GaAs/Si 技术的环境影响，并与现有技术进行了比较。对有关敏感参数和工艺的各种场景进行了建模——例如对几个工业规模的工具进行建模、敏感工艺的能耗、基板重复使用的次数、重新抛光晶圆的频率以及对主要影响驱动因素的改进规模进行基准测试. 分析表明，如果达到预期的工艺效率，与 28% 的 GaAs/Si 模块相比，效率提高 5% 到 20%（转移路线）和 20% 到 30%（直接生长路线，除了臭氧消耗影响）效率为 18% 的单晶模块，适用于所有评估的影响类别——气候变化、土地利用、酸化、臭氧消耗、淡水、海洋、陆地生态毒性、富营养化、人类毒性和光化学氧化。确定的关键热点包括使用金、三氟甲烷 (CHF3) 和 GaAs 晶片。GaAs/Si 纳米线串联模块的 EPBT 介于 1.37（实现的预期工艺效率）和 1.9 年（最坏情况）之间，而单硅模块的 EPBT 为 1.84 年。结果可被视为该技术成功商业化的基准。如果开发出效率为 28% 的 GaAs/Si 纳米线串联模块，则可实现预期的工艺效率，并实现至少 100 次 GaAs 衬底（转移路线）的再利用；然后，在评估的大多数影响类别中，GaAs/Si 模块与效率为 18% 的单硅模块相比表现更好。